There exists many types of two-piece fasteners. By two-piece fastener is in the present context meant a fastening device having two parts that are attached to each other. Usually this type of fastener is used for attachment to a fabric or similar material that is placed between the two parts. One part of the fastening device is provided with a shank or similar member that can penetrate the fabric and this part is placed on one side of the fabric. The other part is provided with a member that can receive and engage with the shank and this part is located on the other side of the fabric. One common two-piece fastener is the rivet type for which a hole is made in the fabric, a shank of the first part is inserted through said hole and the shank is then riveted to the other part on the other side of the fabric. One disadvantage of this rivet fastener is that the fabric is damaged by the hole, and another disadvantage is that a special rivet tool is required for the fastening procedure. For a snap fastener button, which has two fastening devices that can be detachably connected, one riveted fastener is required for each one of the fastening devices.
Another type of two-piece fastener is described in U.S. Pat. No. 5,490,309. The first part is provided with a centrally located shank that has a pointed tip that can puncture the wall of a sock. The shank has a cylindrical shape and is provided with circular notches around its circumference. The second part is located on the other side of the wall of the sock, and it has a centrally located slot with one tongue on each side. When the shank enters between the two tongues, the engagement between the notches and the ends of the tongues prevents separation of the two parts. One of these two-piece fasteners further has a female member and is attached to a sock, and another of these two-piece fasteners has a male member and is attached to another sock, thus providing a snap fastener. The two socks can then be attached to each other by snap connection of the male and female members.
A similar fastener is also known from U.S. Pat. No. 3,699,617, and in this fastener there are two snap fasteners arranged in parallel. The fastener is used for attachment to socks and the shank is relatively thick. A similar idea is also disclosed in US 2007/0256280 and in this document there are four fastening pins distributed on the surface of one of the parts. The fastening pins have a pointed end that can penetrate a sock in order to be inserted into corresponding holes in a second fastener part located on the other side of the sock.